1. Field of the Invention
The present invention generally relates to access data networks that use at least one shared access communication channel to communicate between a plurality of nodes in the network and a terminal to which the plurality of nodes is connected. More specifically, the present invention is intended for synchronizing multiple cable modem termination systems.
2. Description of Related Art
Broadband access technologies such as cable, fiber optic, and wireless have made rapid progress in recent years. There has been a convergence of voice, video, and data networks, which is due in part to the deregulation of the telecommunications industry in the United States. In order to stay competitive, companies offering broadband access technologies need to support voice, video, and other high-bandwidth applications over their local access networks.
One type of broadband access technology relates to cable modem networks. A cable modem network or “cable plant” employs cable modems, which are an advancement of conventional PC data modems and provide high speed connectivity.
FIG. 1 shows a block diagram of a two-way hybrid fiber-coaxial (HFC) cable network 100. As shown in FIG. 1, the cable network 100 includes a head end complex 102. The head end complex 102 may include a plurality of components and/or systems (not shown) such as, for example, a head end, a super head end, a hub, a primary hub, a second hub, etc.
Additionally, as shown in FIG. 1, the head end complex 102 includes cable modem termination system (“CMTS”) 120. Primary functions of CMTS 120 include: (1) receiving data inputs from external sources (such as Internet 122 and satellite system 124); (2) converting the data for transmission over the cable plant; (3) providing appropriate Media Access Control (MAC) level packet headers for data received by the cable system; and (4) modulating and demodulating the data to and from the cable network. Typically, the head end complex 102 is configured to provide a communication interface between nodes (e.g. cable modems) in the cable network and external networks such as, for example, the Internet 122. The cable modems typically reside at the subscriber premises 110A-D.
Existing CMTS devices integrate both upstream channels 126 (for data received from, e.g., subscribers' cable modems) and downstream channels 128 (for data received from, e.g., the Internet 122 or a satellite system 124). Such integration may be accomplished, for example, by including both channels on the same line card. This is desirable, since the downstream provides the timing and control information required for the operation of the upstream.
If the upstream and downstream CMTS could be separated, then much greater flexibility could be achieved and costs could be reduced. Such configurations would allow traffic from the Internet, satellites, etc., passing through a single downstream CMTS to be passed to multiple hubs.